1. Field of the Invention
The present invention relates generally to signal processing, and more specifically, to a method for modulating binary data into audio signals transmitted as sound waves, and for demodulating the data from the sound waves in order to trigger actions at a computing device.
2. Description of the Background
Our music listening experience depends primarily on our sense of hearing, but it can be greatly enhanced by visual sensations. This is clear from live stage shows in which colored stage lighting and lasers are used to enhance the audience's experience. There are prior art systems that imitate a light show on a mobile computing device by direct response to sound vibrations, but the resulting light show is quite random and not well-synchronized to the sound of the music.
What is needed is a system and method to more effectively trigger time-based content via modulated digital communication transmitted through the air via audio waves. Related art includes several systems which allow communication from and/or to smartphones, using audio signals. These systems are inadequate for synchronizing heterogeneous groups of computing devices in noisy environments. Existing systems that modulate frequency or phase are not resilient to environmental noise present in event environments.
Existing systems which modulate amplitude of fewer than 20 frequencies, or a band of less than 2 kilohertz, are not sufficiently resilient to the varying frequency response of mobile computing devices, of which there are hundreds of popular models with many different models of microphone transducer, different operating systems, and different types of processors. Frequency response for these devices is often limited in certain parts of the audio spectrum. Existing amplitude modulation systems are also not resilient to music or other audio that may be playing alongside the audio signal, which may include waves at frequencies which mask the audio signal in its narrow spectral range.
These systems are also inadequate for causing hundreds or thousands of heterogeneous devices to appear to act in a tightly synchronized fashion. For example, an event organizer or sound engineer may want to control the behavior of a large number of mobile computing devices, such as smartphones, to cause the smartphones to flush colors or play sounds in a synchronized fashion, all at the whim of the operator. With the prior art methods, audio signal timing information is not stored precisely, producing a margin of error dependent on the device's audio buffer sizes, context switching algorithm, and other varying factors.
Such synchronization across mobile devices in a physical space is necessary for many spectacular visual effects, and also necessary for reducing audible interference or distortion when the devices emit audio waves. When devices are even a quarter-second off from each other, effects like strobing lights or rapid screen color changes are not visually striking. And when the devices are playing music or sequenced audio, even a tenth of a second of variance can cause even familiar music to sound odd and even unrecognizable.